DESCRIPTION (Applicant's abstract): Stem cells are self-renewing multipotent progenitors with the broadest developmental potential in a given tissue at a given time (Morrison et al. Cell 88:287). There is great interest in neural stem cells because of their importance in neural development and their therapeutic potential. Although neural stem cells have been extensively characterized at the cellular level little is known about how stem cell function is regulated at a molecular level. The recent isolation of uncultured neural crest stem cells (NCSCs) by flow-cytometry (Morrison et al. Cell 96:737) should greatly facilitate such studies by allowing us to focus gene-profiling experiments on a population of cells that is nearly homogeneous with respect to multipotency and self-renewal; furthermore, these cells are known to function as stem cells in vivo. By profiling gene expression in purified, freshly isolated stem cells, we are much more likely to detect patterns of gene expression that regulate important stem cell properties. Specific Aim 1 will be to screen for genes that regulate NCSC self-renewal by analyzing microarrays for genes that hybridize to probe from self-renewing NCSCs but not to probe from NCSCs undergoing lineage commitment. Specific Aim 2 will be to screen for genes that regulate glial lineage specification by analyzing microarrays for genes that hybridize to probe from immature glial progenitors derived from NCSCs but not to probe from self-renewing NCSCs. Finally, although stem cells from different tissues have long been hypothesized to share common regulatory mechanisms this hypothesis has not been systematically tested. Specific Aim 3 will be to test whether there are "stem cell specific" genes by hybridizing probe made from purified NCSCs or purified hematopoietic stem cells (HSCs) to microarrays of ESTs and "HSC-specific" genes. By identifying genes that are expressed by different types of stem cells but not by restricted progenitors, we may identify elements of genetic programs that are conserved between stem cells. By combining the precise tools that are available to study NCSC function at a cellular level with microarray analysis, it will be possible to address fundamental questions about the genetic regulation of neural stem cells.